1. Field of the Invention
The invention relates to thermoplastic multilayer composites having at least one layer, each based on a polyolefin, a polyamide and a polyvinylidene fluoride.
2. Discussion of the Background
Polyolefins, polyvinylidene fluoride and polyamides are each unsuitable for a variety of applications. Although polyamides basically have good mechanical properties, in particular good toughness, for many applications they have poor barrier action. Polar substances can easily migrate through polyamides. This is a problem in the case of fuel lines which carry alcohol-containing fuel.
In contrast, polyvinylidene fluoride has excellent barrier action towards both polar and nonpolar materials. However, a disadvantage of polyvinylidene fluoride is the impact sensitivity. In particular, the notched impact toughness is poor.
Polyolefins have insufficient barrier action towards fuels for a variety of applications. Owning to increased environmental consciousness and the corresponding tightening of legal regulations, single-layer polyolefin pipes cannot be used for transporting of fuels in underground supply lines in petrol stations. Likewise, in the automobile sector, tanks made of polyolefins must be replaced by multilayer tanks having one or more barrier layers, and the various layers must be firmly bonded to each other. However, polyolefins are significantly cheaper than the above-mentioned materials. In addition, the weldability is less problematic. This is a great advantage, particularly for pipes and lines.
Those skilled in the art know that by far the majority of polymers, including polyamide, polyolefins and polyvinylidene fluoride, are incompatible with one another. Sufficient adhesion between the laminated layers is not achieved in the production of multilayer composites. However, a firm bond is absolutely necessary in industrial applications.
Composites of polyamides and polyolefins are known to those skilled in the art. As coupling agents, a series of products are on offer, for example BYNEL.RTM. from DuPont and ADMER.RTM. from Mitsui. These composites too, are not suitable for many applications owing to unsatisfactory paintability and poor barrier action.
It is an object of the present invention to provide a solvent-resistant and temperature-resistant composite of polyvinylidene fluoride and polyolefins.
It is another object to provide a composite which is insensitive to shear stress and has good mechanical properties.
Another objective is to provide a composite with very good adhesion between layers.
Still another objective is that the composite should be able to be produced by means of coextrusion or pressing.
Still another objective is that the composite can be further processed by means of blow moulding, drawing and thermoforming with retention of the good adhesion between layers.